Pre-heat oven to 350 degrees; line a baking sheet with parchment paper and set aside
In a medium bowl, prepare topping; mix together oat flour, oatmeal, brown sugar and cinnamon
Add butter and use fingers to combine until mixture is slightly lumpy
Spread mixture out in parchment paper and bake for 12-14 minutes or until lightly browned; set aside to cool
While crumble is baking, make blueberry sauce
Place blueberries, sugar and lemon juice in a medium pot stove with medium heat
Stir occasionally until some of the berries begin to break down and juice begins to form (~4 minutes)
Turn the heat to high, add cornstarch and stir quickly until sauce reaches desired thickness (1-2 minutes)
Place sauce in refrigerator to cool for 30 minutes
Once ready, finish making ice cream
In the large bowl of an electric mixer with whisk attachment, beat cream on high speed for several minutes, just until stiff peaks form
While whipping cream, in a separate large bowl, stir together sweetened condensed milk and vanilla bean; fold in blueberry sauce
Once cream is ready, fold it into sweetened condensed milk mixture
Pour half of ice cream into a regular-sized loaf pan and drop one third of crumble over top (use fingers to break into pieces); top with remaining ice cream and then with half of remaining crumble; wrap well with seran wrap or tin foil
Freeze for 6 hours or overnight before serving
Use remaining crumble for serving
Notes
Sauce and crumble can be made up to one week before putting ice cream together, refrigerate each in an airtight container until ready to use Blueberry filling from this mixed berry sauce Topping from this fruit crisp
Recipe by Keep It Sweet Desserts at https://www.keepitsweetdesserts.com/no-churn-blueberry-crisp-ice-cream/